feat: add pr, repo, pr_title chat search filters (#25569)

Relates to CODAGT-432

Adds three new search filters to the chat list endpoint (`GET
/api/experimental/chats/`):

- `pr:<number>` - exact PR number match
- `repo:<owner/repo>` - substring match against git remote origin or URL
- `pr_title:<text>` - case-insensitive PR title substring match

Includes SQL filter clauses (EXISTS against `chat_diff_statuses`),
parser with validation, handler wiring, unit tests, swagger annotation
update, and a new search syntax documentation page.

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coderd/database/queries.sql.go

@@ -7638,6 +7638,39 @@ WHERE
         )
         ELSE true
     END
+    -- Filter by PR number (exact match on chat's diff status).
+    AND CASE
+        WHEN $11::int != 0 THEN EXISTS (
+            SELECT 1
+            FROM chat_diff_statuses cds
+            WHERE cds.chat_id = chats_expanded.id
+                AND cds.pr_number = $11
+        )
+        ELSE true
+    END
+    -- Filter by repository (substring match on remote origin or PR URL).
+    AND CASE
+        WHEN $12::text != '' THEN EXISTS (
+            SELECT 1
+            FROM chat_diff_statuses cds
+            WHERE cds.chat_id = chats_expanded.id
+                AND (
+                    cds.git_remote_origin ILIKE '%' || $12 || '%'
+                    OR cds.url ILIKE '%' || $12 || '%'
+                )
+        )
+        ELSE true
+    END
+    -- Filter by pull request title (case-insensitive substring).
+    AND CASE
+        WHEN $13::text != '' THEN EXISTS (
+            SELECT 1
+            FROM chat_diff_statuses cds
+            WHERE cds.chat_id = chats_expanded.id
+                AND cds.pull_request_title ILIKE '%' || $13 || '%'
+        )
+        ELSE true
+    END
     -- Paginate over root chats only. Children are fetched
     -- separately via GetChildChatsByParentIDs and embedded under
     -- each parent. Other callers that need the full set should
@@ -7654,11 +7687,11 @@ ORDER BY
     -chats_expanded.pin_order DESC,
     chats_expanded.updated_at DESC,
     chats_expanded.id DESC
-OFFSET $11
+OFFSET $14
 LIMIT
     -- The chat list is unbounded and expected to grow large.
     -- Default to 50 to prevent accidental excessively large queries.
-    COALESCE(NULLIF($12 :: int, 0), 50)
+    COALESCE(NULLIF($15 :: int, 0), 50)
 `
 
 type GetChatsParams struct {
@@ -7672,6 +7705,9 @@ type GetChatsParams struct {
 	TitleQuery          string                `db:"title_query" json:"title_query"`
 	HasUnread           sql.NullBool          `db:"has_unread" json:"has_unread"`
 	PullRequestStatuses []string              `db:"pull_request_statuses" json:"pull_request_statuses"`
+	PrNumber            int32                 `db:"pr_number" json:"pr_number"`
+	RepoQuery           string                `db:"repo_query" json:"repo_query"`
+	PrTitleQuery        string                `db:"pr_title_query" json:"pr_title_query"`
 	OffsetOpt           int32                 `db:"offset_opt" json:"offset_opt"`
 	LimitOpt            int32                 `db:"limit_opt" json:"limit_opt"`
 }
@@ -7693,6 +7729,9 @@ func (q *sqlQuerier) GetChats(ctx context.Context, arg GetChatsParams) ([]GetCha
 		arg.TitleQuery,
 		arg.HasUnread,
 		pq.Array(arg.PullRequestStatuses),
+		arg.PrNumber,
+		arg.RepoQuery,
+		arg.PrTitleQuery,
 		arg.OffsetOpt,
 		arg.LimitOpt,
 	)